An inverter device rectifies and smooths AC power to generate DC voltage. The DC voltage is supplied to an inverter main circuit, which is then driven. Capacitors having large capacities, such as aluminum electrolytic capacitors, are used as main circuit capacitors for smoothing the DC voltage. The DC power is stored in the main circuit capacitors even when the inverter device has been powered off. Accordingly, there is a possibility of electrical shock when the inverter device is touched.
To discharge electric power stored in the main circuit capacitors, the conventional art uses discharge resistors connected in parallel to the main circuit capacitors to reduce a discharge time during power-off. However, this results in discharge even during power supply, so a large resistance value is required so that an amount of discharge is rendered small during a normal operation after power supply. Thus, the above-described arrangement cannot reduce the discharge time during power-off cannot be reduced. Furthermore, rendering the resistance value smaller increases unnecessary loss in normal operation despite reducing the discharge time.
For example, when a plurality of capacitors is series-connected for use as main circuit capacitors, balancing resistors are sometimes connected in parallel to the main circuit capacitors to balance voltages applied to the main circuit capacitors respectively. In this case, even though combination use of the balancing resistors as discharge resistors can be considered, the discharge resistors are normally connected to the main circuit capacitors as described above, causing unnecessary loss in normal operation.